CN112415327B - Cable distribution network fault section identification method based on grounding wire current direction difference - Google Patents
Cable distribution network fault section identification method based on grounding wire current direction difference Download PDFInfo
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- CN112415327B CN112415327B CN202011136605.5A CN202011136605A CN112415327B CN 112415327 B CN112415327 B CN 112415327B CN 202011136605 A CN202011136605 A CN 202011136605A CN 112415327 B CN112415327 B CN 112415327B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/088—Aspects of digital computing
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Abstract
The invention discloses a cable distribution network fault section identification method based on grounding wire current direction difference, which is suitable for being used in a power system. After a power distribution network fault is detected, acquiring the current of a grounding wire at the head end of each section of cable in the whole network, and judging a fault outgoing line; acquiring the current of a grounding line at the head end of each section of cable of a fault outgoing line; if the system neutral point is arc-extinguished and grounded, filtering the low-frequency component of all the measured ground line currents to only reserve the high-frequency component, and if the system neutral point is not grounded, directly using the measured ground line currents; taking the current direction of the grounding wire of the first section of the measured cable as a reference, and determining the current direction of the grounding wire at the head end of the rest cable on the fault outgoing line; and finally, determining a fault path according to the current direction of the grounding wire and the network topology structure, wherein the fault cable section is positioned at the tail end of the obtained fault path. The method has high effectiveness and robustness, and is adaptive to the grounding arc fault of the distribution cable.
Description
Technical Field
The invention relates to a cable distribution network fault section identification method, in particular to a cable distribution network fault section identification method based on grounding wire current direction difference and suitable for being used in a power system.
Background
With the continuous development of urban distribution networks, the influence on urban appearances is small due to less demand on land, and the distribution lines mainly adopt three-core underground cables. For example, in the city centers of large cities in china such as beijing, shanghai, etc., more than 98% of overhead transmission lines have been replaced by underground cables. However, the three-core underground cable is prone to malfunction due to adverse factors such as external forces or internal defects. The quick and reliable fault section positioning is beneficial to accelerating fault isolation, reducing power failure time and ensuring the stability and safety of the whole network.
When the distribution line has a fault, the voltage and the current of the distribution line deviate from the normal voltage and the normal current, and a basis is provided for identifying a fault line section. Current research has shown that fault zone identification techniques have demonstrated good performance in power distribution networks dominated by overhead lines. However, in underground distribution cable systems, the fault zone identification method has not been fully developed.
Three-core cables are typically laid underground, the three-phase wires are surrounded by insulating rubber, and some types of smart meters (such as uPMUs or fault indicators) cannot be installed along the cable. Although phase currents and voltages are not easily available in a three-wire cable, the current of the ground wire of the cable can be measured only by a common measuring unit. Therefore, the method for identifying the single-phase fault section of the power distribution network based on the simple cable grounding wire current information research principle and strong practicability has theoretical research value and has important practical significance for engineering practice.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the defects of the technical problems, the cable distribution network fault section identification method based on the grounding wire current direction difference is simple in step, good in judgment effect and capable of accurately identifying the fault cable line.
In order to achieve the technical purpose, the method for identifying the fault section of the cable distribution network based on the current direction difference of the grounding wire is suitable for M sections of cable lines in the distribution network, and the head end of each cable line is provided with a grounding wire current measuring point, and the method comprises the following steps:
a, when the power distribution network has a fault, obtaining the current i on the grounding wire of the head end of the power distribution cable line q by a measuring point at the grounding wire of the head end of the cable lineq(q＝1,2,...,M)；
b, acquiring current information of the grounding wires at the head ends of all the distribution cable lines, classifying according to the outgoing lines, taking the direction of any one grounding wire as a reference, and determining the current direction of the grounding wires at the head ends of the rest cable lines of the distribution network by utilizing the Pearson correlation coefficient so as to obtain the current direction of the grounding wires at the head ends of all the cable lines;
c, determining the grounding mode of the neutral point of the power grid, if the neutral point is grounded through an arc suppression coil, processing all grounding wire currents by using a band-pass filter, and recording the filtered head end grounding wire current as i for any cable qqfIf the neutral point of the power grid is not grounded, the acquired current of the grounding wire does not need to be processed;
d, determining a fault path by combining a network topological structure according to the current direction of the grounding wire of each section of cable line, and further determining a fault cable line;
if the neutral point of the power distribution network is grounded through the arc suppression coil, the obtained current of the grounding wire needs to be subjected to band-pass filtering, in the step c, the lower limit of the passband of the filter is set to be 250Hz, and the upper limit is set to be 750 Hz; the lower limit frequency of the cutoff band is 150Hz, and the upper limit is 1 kHz.
The fault path in step d has the following characteristics: the fault path comprises at least one cable line, all the cable lines contained in the fault path are continuously distributed in an end-to-end connection mode in the power distribution network topology, and the current directions of the grounding wires at the head ends of all the cable lines contained in all the fault paths are consistent; the faulty cabling corresponds to the very end of the faulty path, i.e. the cabling furthest away from the busbar.
Has the advantages that:
compared with the prior art, the method and the device have the advantages that the fault section of the cable distribution network is positioned only by using the current signal of the grounding wire, zero sequence current does not need to be measured, each measuring point does not need to be accurately synchronized, the influence of arc faults is avoided, the field implementation is simple, the detection speed is high, the accuracy rate is high, and the engineering practice value is very high.
Drawings
Fig. 1 is a schematic flow chart of a cable distribution network fault section identification method based on the difference of the direction of the grounding line current according to the present invention;
FIG. 2 is a schematic diagram of a typical radial distribution cable network topology;
FIG. 3 is a schematic diagram of the established fault simulation model of the 10kV cable type power distribution network
Detailed Description
The invention will be further described with reference to the accompanying drawings in which:
as shown in fig. 1, the method for identifying a cable distribution network fault section based on the difference of the current directions of the ground wires by using the time domain characteristics of the current of the wide-area ground wire is suitable for M cable lines in total in the distribution network, and the head end of each cable line is provided with a ground wire current measuring point, which comprises the following steps:
a, when the power distribution network has a fault, obtaining the current i on the grounding wire of the head end of the power distribution cable line q by a measuring point at the grounding wire of the head end of the cable lineq(q＝1,2,...,M)；
b, acquiring current information of the grounding wires at the head ends of all the distribution cable lines, classifying according to the outgoing lines, taking the direction of any one grounding wire as a reference, and determining the current direction of the grounding wires at the head ends of the rest cable lines of the distribution network by utilizing the Pearson correlation coefficient so as to obtain the current direction of the grounding wires at the head ends of all the cable lines;
c, determining the grounding mode of the neutral point of the power grid, if the neutral point is grounded through an arc suppression coil, processing all grounding wire currents by using a band-pass filter, and recording the filtered head end grounding wire current as i for any cable qqfIf the neutral point of the power grid is not grounded, the acquired current of the grounding wire does not need to be processed; the lower limit of the filter passband is set to 250Hz, and the upper limit is set to 750 Hz; the lower limit frequency of the cut-off band is 150Hz, and the upper limit is 1kHz
d, determining a fault path by combining a network topological structure according to the current direction of the grounding wire of each section of cable line, and further determining a fault cable line; the fault path in step d has the following characteristics: the fault path comprises at least one cable line, all the cable lines contained in the fault path are continuously distributed in an end-to-end connection mode in the power distribution network topology, and the current directions of the grounding wires at the head ends of all the cable lines contained in all the fault paths are consistent; the faulty cabling corresponds to the very end of the faulty path, i.e. the cabling furthest away from the busbar.
Example one
1) After the power distribution network fails, a total M-section cable line of the whole network is set to be provided with a grounding wire current measuring point, and a measuring point at the grounding wire at the head end of the power distribution cable line obtains a fault current i on the grounding wire at the head end of the power distribution cable line of the whole networkqs_af(t)(q＝1,2,...,M)；
2) For the measured current i of the first end grounding wire of the whole network cable lineqs_af(t) classifying according to the outgoing lines, taking the direction of any one of the current of the ground lines as a reference, determining the current direction of the ground line at the head end of the residual cable in the whole network by utilizing the Pearson correlation coefficient, further obtaining the current direction of the integral ground line of each outgoing line, and selecting the line with the current direction of the ground line different from that of other outgoing lines as a fault outgoing line by comparison according to the current direction of the integral ground line of each outgoing line, wherein the formula is as follows:
Dir(ips_af(t))＝-Dir(iqs_af(t))
the Dir () function represents the direction of current, ips _ af (t) and iqs _ af (t) respectively represent the current direction of the overall grounding wire of the fault cable outgoing line p and the current direction of the overall grounding wire of the sound cable outgoing line q, and the current directions of the two are opposite;
3) after the fault outgoing line is determined, N sections of cables on the fault outgoing line are configured with ground line current measuring points, and the fault current i on the ground line at the head end of each cable of the fault outgoing line whole line is obtained according to the ground line current information at the head end of the whole network cable obtained in the step 1)ks_af(t)(k＝1,2,...,N)；
4) If the neutral point of the power grid is grounded through the arc suppression coil, all the obtained grounding line current is processed through the band-pass filter, wherein the lower limit of the filter passband is set to be 250Hz, and the upper limit is set to be about 750 Hz; the lower limit frequency of the cutoff band is 150Hz, the upper limit is about 1kHz, and the filtered head end earth wire current is represented as i for any cable kks_fil_af(t) if not, using only the ground line current i sampled initially per cableks_af(t)；
5) Grounding wire current i of first-section cable leading out by faultks_af(t) (or ground line current i after filtering in arc suppression coil grounding systemks_fil_af(t)) taking the direction as a reference (k is 1), and determining the current direction of the grounding wire at the head end of the residual cable on the fault outgoing line by using a Pearson correlation coefficient;
6) according to the current direction of each section of cable grounding wire of the fault outgoing line, a network topological structure is combined, a transformer substation bus starts until the current direction of a certain section of cable line is different from the current direction of the first section of cable grounding wire of the outgoing line, a fault path is determined, the fault cable is located at the tail end of the fault path, and the formula is as follows:
Dir(ijs_af(t))＝-Dir(iks_af(t))
wherein, Ijs_af(t) and iks_af(t) represents the direction of the current of the earth wire of the faulty cable segment j and the direction of the current of the earth wire of the robust cable segment k, respectivelyThe flow direction is reversed.
Simulation verification
The topological structure of a typical radial distribution cable network is shown in fig. 2, various faults are simulated in a typical 10kV three-phase distribution cable network established by a PSCAD/EMTDC, and the schematic diagram of a simulation model is shown in fig. 3. A frequency-dependent characteristic model of the three-core cable is established, and the length information of each section of cable is shown in table 1.
TABLE 1 Length information of the sections of Cable
Switch K1 determines the neutral grounding mode of the system. CB1 and CB2 are circuit breakers connecting three-segment bus bars. The CB3, the CB4 and the CB5 are circuit breakers in the ring main unit. In normal operation, CB1 and CB2 are closed, and CB3, CB4 and CB5 are disconnected. All cables passing through a ground resistor R at both endsSGGround as shown in fig. 3. The arc suppression coil inductance value is selected based on a 10% compensation. The sampling rate was set to 5 kHz. The earth wire current at the head end of each cable section is recorded by a corresponding meter. Fault simulations have been performed in the above-described cable network in various situations. The detailed simulation results for these failure cases are shown in tables 2 and 3.
TABLE 2 information of the failure conditions and the identification results of the failed sections
TABLE 3 Fault zone identification results set to Cable arcing faults
Where # n denotes the corresponding cable number (n ═ 1,2, …, 24); rfRepresenting a fault point transition resistance; thetafRepresenting a fault initial phase angle; UNG denotes that the neutral point is not grounded; ASG represents that a neutral point is grounded through an arc suppression coil;isnrepresenting the ground line current at the n head end of the cable segment on the corresponding fault path.
As can be seen from the table: the method provided by the invention has better identification precision for fault sections with different single-phase earth faults and arc faults in a radial power distribution network with a three-core cable.
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.
Claims (2)
1. Cable distribution network fault section identification method based on grounding wire current direction difference and applicable to common fault sections in distribution networkMThe method is characterized in that the method comprises the following steps:
a, when the power distribution network fails, acquiring the power distribution cable line from a measuring point at the grounding wire at the head end of the cable lineqCurrent on head end earth wirei q (q=1,2,...,M)；
b, acquiring current information of the grounding wires at the head ends of all the distribution cable lines, classifying according to the outgoing lines, taking the direction of any one grounding wire as a reference, and determining the current direction of the grounding wires at the head ends of the rest cable lines of the distribution network by utilizing the Pearson correlation coefficient so as to obtain the current direction of the grounding wires at the head ends of all the cable lines; according to the current direction of the integral grounding wire of each outgoing wire, selecting a circuit with the grounding wire current direction different from that of other outgoing wires as a fault outgoing wire by comparison, wherein the formula is as follows:
wherein the function Dir () represents the direction of the current,i ps_af (t) Andi qs_af (t) Cable outlet for respectively indicating faultpOf (2)Body earth wire current direction and sound cable outletqThe current directions of the whole grounding wire are opposite;
c, determining the grounding mode of the neutral point of the power grid, if the neutral point is grounded through an arc suppression coil, processing all grounding wire currents by using a band-pass filter, and for any cableqAnd the filtered head end earth line current is recorded asi qf If the neutral point of the power grid is not grounded, the acquired current of the grounding wire does not need to be processed;
d earth wire current of first section cable of outlet wire with faulti ks af_(t) Is taken as a referencekDetermining the current direction of a grounding wire at the head end of a residual cable on a fault outgoing line by using a Pearson correlation coefficient; determining a fault path according to the current direction of the grounding wire of each section of cable line, and further determining a fault cable line;
starting from a transformer substation bus until the current directions of a certain section of cable line and the first section of outgoing cable grounding wire are different, determining a fault path, wherein the formula is as follows:
wherein the content of the first and second substances,i js af_(t) Andi ks af_(t) Respectively indicating faulty cable sectionsjCurrent direction of earth wire and sound cable sectionkThe current directions of the grounding wire and the grounding wire are opposite;
the fault path comprises at least one cable line, all the cable lines contained in the fault path are continuously distributed in an end-to-end connection mode in the power distribution network topology, and the current directions of the grounding wires at the head ends of all the cable lines contained in all the fault paths are consistent; the faulty cabling corresponds to the very end of the faulty path, i.e. the cabling furthest away from the busbar.
2. The method for identifying fault sections of a cable distribution network based on the difference of the current directions of the grounding wires according to claim 1, wherein the method comprises the following steps: if the neutral point of the power distribution network is grounded through the arc suppression coil, the obtained current of the grounding wire needs to be subjected to band-pass filtering, in the step c, the lower limit of the passband of the filter is set to be 250Hz, and the upper limit is set to be 750 Hz; the lower limit frequency of the cutoff band is 150Hz, and the upper limit is 1 kHz.
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